|1.Research Institution||Tohoku University|
|150th Committee on Acoustic Wave Device Technology|
|3.Term of Project||FY 1997 〜 FY 2001|
|5.Title of Project||Investigation of New High Performance Piezoelectric Single Crystals and Thin Films, and Applications for Next Generation Electronics and Communication Systems|
|Name||Institution,Department||Title of Position|
|Ken Yamada||Tohoku University, Graduate School of Engineering||Associate Professor|
|Names||Institution,Department||Title of Position|
|Kiyoshi Nakamura||Tohoku University, Graduate School of Engineering||Professor|
|Kazuhiko Yamanouchi||Tohoku Institute of Technology, Electronic Engineering||Professor|
|Kazuo Tsubouchi||Tohoku University, Research Institute of Electrical Communication||Professor|
8.Summary of Research Results
The purpose of this research is to investigate on new high performance piezoelectric single crystals and thin films and their application for next generation electronics and communication systems. The main results of this research are summarized below.
1. The BGS surface wave of ultra high coupling (k2=0.54) was found to exist on Z-axis cylinder cuts of KNbO3. Large size KNbO3 single crystals were grown using a TSSG method. The efficiency of the convolver using 45° Y-XKNbO3 was found to be 25dB higher than that of the Y-ZLiNbO3 convolver. The collinear interaction of the BGS wave with optical waves was theoretically analyzed. It offers very efficient TE-to-TM optical mode conversion, thereby yielding an efficient tunable optical filter.
2. The orientation dependence of coupling factors for various modes of vibrations in KNbO3 was calculated. Especially, the coupling factor kt for the thickness-extensional mode was found to be 70% for the 49.5°-rotated X-cut, which is the highest among known piezoelectrics.
3. ZnO films with the c axis lying in the film plane were found to be epitaxially grown rotated Y-cuts of LiTaO3 by ECR-MBE. The SH-SAW in the (110)ZnO/42°Y-X LiTaO3 showed a high coupling factor due to the piezoelectric contribution of LiTaO3 and ZnO. Ferroelastic and ferroelectric Ta2O5 thin films useful for SAW devices were also obtained by a new linear rapid thermal annealing technique. The maximum value of the electromechanical coupling factor for the SAW was 4.56%.
4. A 2.4GHz AlN/Al2O3 surface-acoustic-wave matched filter was developed. Using it, we have designed and implemented a spread-spectrum (SS) wireless switch system and a packet spread-spectrum code-division multiple-access (SS-CDMA) system.
5. The leaky SAW on SiO2/LiNbO3 was found to have a large k2 of leaky SAW over 0.2 and zero propagation attenuation for the metallized surface at H/λ≒0.15〜0.2 (H:SiO2 film thickness). This substrate makes it possible to obtain wide band SAW filters and VCOs.
6. A new type of piezoelectric film resonator using λ/4 acoustic multilayers was investigated theoretically and experimentally. As a result this new type of resonator was demonstrated to be promising as a communication device in a super high frequency range from 1 to 20GHz.
7. The propagation characteristics of Rayleigh waves and leaky surface acoustic waves in La3Ga5SiO14 were theoretically investigated for all cuts and propagation directions. The maximum value of k2 with a zero TCD was 0.5% for Rayleigh wave on (0°, 149.16°, 24°) -cut.
8. Fast and precise simulation techniques were established for the design of SAW single-phase unidirectional transducers and RF devices employing shear-horizontal-type SAWs.
(1)Acoustic wave devices、(2)Piezoelectric single crystals、(3)Piezoelectric thin films
(4)SAW convolver、(5)SAW matched filter、(6)Piezoelectric thin film resonator